Exhaust gas purifying system

ABSTRACT

An exhaust gas purifying system is used for purifying exhaust gas discharged from an internal combustion engine installed in a vehicle. The exhaust gas purifying system includes an electrochemical device and a control device. The electrochemical device includes an anode, a cathode and an electrolyte layer disposed between the anode and the cathode. The control device is operable to control the internal combustion engine and the electrochemical device. The control device receives data on condition of the internal combustion engine and controls amount of electric current to be supplied to the electrochemical device based on the data. The data represents amount of exhaust gas. When the control device recognizes that the amount of exhaust gas is increased, the control device increases the amount of electric current to be supplied to the electrochemical device.

BACKGROUND OF THE INVENTION

The present invention relates to an exhaust gas purifying system.

In a known purifying system, a diesel particulate filter (DPF) or aselective catalytic reduction (SCR) catalyst with urea is used forpurifying exhaust gas discharged from an internal combustion engineinstalled in a vehicle. Some of the systems are operable to control thepurifying capacity in accordance with conditions of exhaust gas byadjusting the temperature of the system or of exhaust gas.

Such a system controlling its purifying capacity by adjusting thetemperature is disclosed in Japanese Unexamined Patent ApplicationPublication No. 2004-124855. The publication discloses post fuelinjection or delayed fuel injection performed for increasing the DPFtemperature thereby to increase the exhaust gas purifying capacity. Onthe other hand, an intake throttle is fully opened for decreasing theDPF temperature thereby to decrease the exhaust gas purifying capacity.

In a conventional exhaust gas purifying system, however, it has beendifficult to accurately control the purifying capacity. In the abovesystem disclosed in the reference No. 2004-124855, for example, a timelag occurs from the time when adjusting temperature is performed to thetime when the temperature is actually increased as controlled. Inaddition, the system is susceptible to errors due to externaldisturbances. Therefore, it is difficult for such system to ensure thecontrolling accuracy. Particularly, since the system controls factorsthat are related to the internal combustion engine such as the fuelinjection and the intake throttle, it is difficult for the system tocontrol the purifying capacity without taking account of runningconditions of the vehicle.

The present invention is directed to providing an exhaust gas purifyingsystem so as to easily and accurately control the exhaust gas purifyingcapacity without affecting running conditions of the vehicle.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, an exhaust gaspurifying system is used for purifying exhaust gas discharged from aninternal combustion engine installed in a vehicle. The exhaust gaspurifying system includes an electrochemical device and a controldevice. The electrochemical device includes an anode, a cathode and anelectrolyte layer disposed between the anode and the cathode. Thecontrol device is operable to control the internal combustion engine andthe electrochemical device. The control device receives data oncondition of the internal combustion engine and controls amount ofelectric current to be supplied to the electrochemical device based onthe data. The data represents amount of exhaust gas. When the controldevice recognizes that the amount of exhaust gas is increased, thecontrol device increases the amount of electric current to be suppliedto the electrochemical device.

Other aspects and advantages of the invention will become apparent fromthe following description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. The inventiontogether with objects and advantages thereof, may best be understood byreference to the following description of the presently preferredembodiments together with the accompanying drawings in which:

FIG. 1 is an illustrative view showing an arrangement of an exhaust gaspurifying system and the related devices according to a first preferredembodiment of the present invention;

FIG. 2 is a schematic view of an electrochemical device according toFIG. 1; and

FIG. 3 is an illustrative view showing the operation of theelectrochemical device of FIG. 1 in purifying exhaust gas.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe the first preferred embodiment of thepresent invention with reference to FIGS. 1 through 3. FIG. 1 shows anarrangement of an exhaust gas purifying system 120 and the relateddevices according to the first preferred embodiment. The exhaust gaspurifying system 120 is used for purifying exhaust gas discharged froman internal combustion engine 100 installed in a vehicle. Thepurification is achieved by decomposing nitrogen oxides (NOx) andparticulate matters (PM) contained in the exhaust gas as will bedescribed below.

As shown in FIG. 1, an exhaust passage pipe 110 is connected to theinternal combustion engine 100. The exhaust gas purifying system 120 isdisposed in the middle of the exhaust passage pipe 110. Exhaust gasdischarged from the internal combustion engine 100 into the exhaustpassage pipe 110 passes through the exhaust gas purifying system 120.Then, purified gas is discharged out from the exhaust passage pipe 110.The exhaust gas purifying system 120 includes a plurality ofelectrochemical devices 10. The electrochemical device 10, which isknown also as an electrochemical reactor, is used for purifying exhaustgas by electrochemical reaction. The electrochemical reaction performsby supplying electric current from an external battery. Theelectrochemical device 10 includes an anode 20, a cathode 22 and anelectrolyte layer 24 disposed between the anode 20 and the cathode 22.The electrochemical device 10 is a plate-like shaped and has the anode20 and the cathode 22 on the opposite surfaces thereof.

Each electrochemical device 10 is spaced apart at a predeterminedinterval in the same orientation such that each surface of theelectrodes of the electrochemical devices 10 is parallel to the flowdirection of exhaust gas. Specially, the anode 20 and the cathode 22 ofany two adjacent electrochemical devices 10 face and extend parallel toeach other. Such arrangement of the electrochemical devices 10 allowsthe exhaust gas to pass through the spaces between the each anode 20 andthe cathode 22 in the exhaust gas purifying system 120.

FIG. 2 is a schematic view of one of the electrochemical devices 10. Theelectrochemical device 10 is electrically connected at the anode 20 andthe cathode 22 to an external battery 30. The anode 20 of theelectrochemical device 10 is connected to the positive electrode of thebattery 30, while the cathode 22 of the electrochemical device 10 isconnected to the negative electrode of the battery 30. The electrolytelayer 24 of the electrochemical device 10 includes electrolyte andallows ions to move between the anode 20 and the cathode 22.

The anode 20 and the cathode 22 of the electrochemical device 10 aremade of materials functioning as the respective electrodes. For example,the anode 20 is made of a screen-printed platinum (Pt) based materialwhile the cathode 22 is made of a screen-printed nickel (Ni) basedmaterial. The electrolyte layer 24 is made of ion-conductive electrolytematerial such as yttria-stabilized zirconia (YSZ) so as to conductproton or oxygen ion. The electrochemical device 10 operates mosteffectively under a temperature in the range between 600 and 800 degreesCelsius. The optimal temperature range varies depending on the chemicalcomposition of the electrolyte layer 24.

Referring to FIG. 1, the internal combustion engine 100 and the exhaustpassage pipe 110 are provided with detectors for detecting various dataon condition of the internal combustion engine 100. The detectorsinclude an engine speed sensor 41, an accelerator position sensor 42, athrottle position sensor 43, an oxygen sensor 44 and a temperaturesensor 45. The engine speed sensor 41, the accelerator position sensor42 and the throttle position sensor 43 are mounted to the internalcombustion engine 100. The speed sensor 41 detects the engine speed ofthe internal combustion engine 100. The accelerator position sensor 42detects the accelerator pedal position. The throttle position sensor 43detects the throttle valve opening. The oxygen sensor 44 and thetemperature sensor 45 are mounted to the exhaust passage pipe 110. Theoxygen sensor 44 detects the oxygen concentration in exhaust gas. Thetemperature sensor 45 detects the exhaust gas temperature. Each of thesensors 41 through 45 does not necessarily have to be located at theposition as described above and illustrated in FIG. 1. The acceleratorposition sensor 42 and the throttle position sensor 43 may be mounted toan accelerator pedal and a throttle valve respectively. In theillustrated embodiment, the oxygen sensor 44 and the temperature sensor45 are mounted to the exhaust passage pipe 110 on the side upstream ofthe exhaust gas purifying system 120 as viewed in the direction of theflow of exhaust gas. Alternatively, the sensors 44, 45 may be arrangedon the opposite side downstream of the exhaust gas purifying system 120.

The vehicle is provided with an engine control unit (ECU) 50 serving asa control device receiving the data from the sensors 41 through 45. TheECU 50 is electrically connected to each of the engine speed sensor 41,the accelerator position sensor 42, the throttle position sensor 43, theoxygen sensor 44 and the temperature sensor 45 so as to receive thedata. The ECU 50 receives the data from the sensors 41 through 45periodically, for example, at every second.

The ECU 50 is also electrically connected to each of the electrochemicaldevices 10 for controlling its performance by regulating the amount ofelectric current to be supplied to each of the electrochemical devices10 according to the data that represents the condition of the internalcombustion engine 100. The electric current control is accomplished bychanging the state of an electrical circuit connecting the battery 30and the electrochemical device 10 periodically, for example, at everyone second.

Each of the detected values has a positive correlation with the amountof exhaust gas. That is, the amount of exhaust gas is increased with anincrease of the engine speed, the accelerator pedal position, thethrottle valve opening, the oxygen concentration in exhaust gas and theexhaust gas temperature, and vice versa.

The ECU 50 controls the operation of the electrochemical device 10 in away that the amount of electric current to be supplied to theelectrochemical device 10 is increased in accordance with an increase ofthe amount of exhaust gas. Namely, when the data represents an increaseof the amount of exhaust gas, the ECU 50 recognizes a state that theamount of exhaust gas is increased and increases the amount of electriccurrent to be supplied to the respective electrochemical devices 10. Onthe other hand, when the data represents a decrease of the amount ofexhaust gas, the ECU 50 recognizes a state that the exhaust gas isdecreased and decreases the amount of electric current to be supplied tothe respective electrochemical devices 10. In other words, the ECU 50controls the amount of electric current to be supplied to theelectrochemical device 10 in such a manner that the amount of electriccurrent is a monotonically increasing function of each value of theengine speed, the accelerator pedal position, the throttle valveopening, oxygen concentration in exhaust gas and exhaust gastemperature. The functional relation between the amount of electriccurrent supplied to the electrochemical device 10 and each of the values(engine speed, accelerator pedal position, throttle valve opening,oxygen concentration in exhaust gas and exhaust gas temperature) can bespecified based on experimental results and the like.

Referring to FIG. 1, the ECU 50 is connected to the electrochemicaldevices 10 in such a way that the ECU 50 controls the respectiveelectrochemical devices 10 individually. Alternatively, the ECU 50 maybe connected in such a way that the ECU 50 controls a plurality of orall of the electrochemical devices 10 collectively. Furthermore, the ECU50 also serves as a common ECU for controlling other various operationsof the vehicle.

The following will describe the operation of the exhaust gas purifyingsystem 120. Referring to FIG. 1, exhaust gas produced by running theinternal combustion engine 100 is discharged and flows into the exhaustgas purifying system 120 through the exhaust passage pipe 110. Then, theexhaust gas flows inside the exhaust gas purifying system 120 in contactwith or flowing through spaces around the surfaces of the anode 20 andthe cathode 22 of the electrochemical devices 10. While the exhaust gasis passing through the exhaust gas purifying system 120, PM and NOxcontained in the exhaust gas are decomposed with the result that theexhaust gas is purified.

FIG. 3 shows the operation of the electrochemical device 10 in purifyingexhaust gas. Carbon in PM contained in exhaust gas is reacted on oraround the surface of the anode 20 with oxygen ions conducted throughthe electrolyte layer 24 thereby to produce carbon dioxide andelectrons. Electrons are attracted by the positive electrode of thebattery 30 and moved to the battery 30. Carbon dioxide is discharged outof the exhaust passage pipe 110 to the atmosphere. PM is thus decomposedat the anode 20, with the result that the exhaust gas is purified.Nitrogen oxides (NOx) in the exhaust gas are reacted on or around thesurface of the cathode 22 with electrons supplied from the battery 30thereby to produce oxygen ions and nitrogen. Oxygen ions are attractedby the anode 20 of the electrochemical device 10 and moved through theelectrolyte layer 24. Nitrogen is discharged out of the exhaust passagepipe 110 to the atmosphere. NOx is thus decomposed at the cathode 22,with the result that the exhaust gas is purified.

It is noted that the performance of the electrochemical device 10, whichis the exhaust gas purifying capacity, depends on the amount of electriccurrent supplied to the electrochemical device 10. The larger the amountof electric current from the anode 20 to the cathode 22 through theelectrolyte layer 24 is, the higher the capacity to decompose PM and NOxin exhaust gas is. Consequently, the larger amount of exhaust gas ispurified.

The following will describe the control by the ECU 50 and the processfor purifying exhaust gas in the exhaust gas purifying system 120. Whilethe vehicle is running under a normal condition, the internal combustionengine 100 is also running under a normal condition and the data isalmost constant. In such a case, the ECU 50 maintains the amount ofelectric current to be almost constant. When the vehicle driver operatesthe accelerator to change the position, for example, to increase theengine speed. Then, the engine speed sensor 41 and the acceleratorposition sensor 42 detect the changes respectively and the datarepresenting such changes are inputted into the ECU 50. Since the datarepresent an increase of amount of exhaust gas, the ECU 50 increases theamount of electric current to be supplied to the electrochemical device10. As a result, the exhaust gas purifying capacity of theelectrochemical device 10 is increased. In this way, purifying ofincreased amount of exhaust gas is accomplished appropriately.

As described above, the exhaust gas purifying system 120 according tothe preferred embodiment includes the electrochemical devices 10 and theECU 50. The ECU 50 is operable to control the exhaust gas purifyingcapacity by changing the amount of electric current to be supplied tothe electrochemical device 10 based on the data on the conditions of theinternal combustion engine 100. Thus, controlling of the exhaust gaspurifying capacity of the exhaust gas purifying system 120 is achievedeasily and accurately.

Since it is easy to control the amount of electric current, the exhaustgas purifying system 120 of the present invention is capable ofcontrolling the exhaust gas purifying capacity more easily andaccurately as compared with the conventional systems that control thesystem temperature or exhaust gas temperature for purification ofexhaust gas. Furthermore, the exhaust gas purifying system 120 of thepresent invention is capable of avoiding damages caused by heatgenerated in the system. More advantageously, the exhaust gas purifyingsystem 120 controlling the amount of electric current will not affectrunning conditions of other vehicle equipments such as electronic fuelinjection system and, therefore, it contributes to fuel consumption.

In the above-described preferred embodiment, the data includes enginespeed, accelerator pedal position, throttle valve opening, oxygenconcentration in the exhaust gas and exhaust gas temperature. Inaddition, the data may include other data such as the amount of PM orNOx concentration in exhaust gas. For example, a sensor for detectingthe amount of PM or NOx concentration in the exhaust gas may be providedin the exhaust passage pipe 110 to control the amount of electriccurrent to be supplied to the electrochemical device 10 based on thedetected amount of PM or NOx concentration. In this case, the ECU 50operates such that the amount of electric current is increased inaccordance with an increase of the detected amount of PM or NOxconcentration. Alternatively, an acceleration sensor for detectingaccelerated velocity may be installed in the vehicle to control theamount of electric current to be supplied to the electrochemical device10 depending on the detected velocity. In this case, the ECU 50 isoperated such that the amount of electric current is increased with anincrease of the detected velocity. The data may include further othervalues such as those indicative of the so-called operating modes of thevehicle.

Also in the above-described preferred embodiment, the ECU 50 operable tocontrol the exhaust gas purifying capacity by changing the amount ofelectric current to be supplied to the electrochemical device 10.Alternatively, the ECU 50 may be operable to control the exhaust gaspurifying capacity by changing the voltage to be applied across theelectrochemical devices 10 of the exhaust gas purifying system 120.

Therefore, the present examples and embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein but may be modified within the scope of theappended claims.

1. An exhaust gas purifying system for purifying exhaust gas dischargedfrom an internal combustion engine installed in a vehicle, comprising:an electrochemical device including an anode, a cathode and anelectrolyte layer disposed between the anode and the cathode; and acontrol device operable to control the internal combustion engine andthe electrochemical device; wherein the control device receives data oncondition of the internal combustion engine and controls amount ofelectric current to be supplied to the electrochemical device based onthe data.
 2. The exhaust gas purifying system according to claim 1,wherein the data represents amount of exhaust gas, wherein when thecontrol device recognizes that the amount of exhaust gas is increased,the control device increases the amount of electric current to besupplied to the electrochemical device, and when the control devicerecognizes that the amount of exhaust gas is decreased, the controldevice decreases the amount of electric current to be supplied to theelectrochemical device.
 3. The exhaust gas purifying system according toclaim 1, wherein the electrochemical device is a plate-like shaped andhas the anode and the cathode on the opposite surfaces thereof, theelectrolyte layer allows ions to move between the anode and the cathode.4. The exhaust gas purifying system according to claim 1, wherein thedata is at least one of an engine speed, an accelerator pedal position,a throttle valve opening, oxygen concentration in exhaust gas andexhaust gas temperature.
 5. The exhaust gas purifying system accordingto claim 1, wherein the anode is made of platinum based material.
 6. Theexhaust gas purifying system according to claim 1, wherein the cathodeis made of nickel based material.
 7. The exhaust gas purifying systemaccording to claim 1, wherein the exhaust gas purifying system having aplurality of electrochemical devices which are placed in an exhaustpassage pipe at a predetermined interval each other in the sameorientation such that each surface of the anode and the cathode isparallel to the exhaust gas flow.
 8. An exhaust gas purifying method forpurifying exhaust gas discharged from an internal combustion engineinstalled in a vehicle, wherein the exhaust gas purifying systemincluding an electrochemical device having an anode, a cathode and anelectrolyte layer disposed between the anode and the cathode comprisingsteps of: detecting data on condition of the internal combustion engineand controlling amount of electric current to be supplied to theelectrochemical device based on the data.